President-elect Donald Trump has vowed to move the U.S. Embassy in Israel from Tel Aviv to Jerusalem, a move which would break with longstanding American policy. His proposal has touched off debate on one of the most emotional and contentious issues dividing Israelis and Palestinians: The status of the city they both regard as their capital.

In 1947, at the end of the British mandate in Palestine, the United Nations adopted a resolution calling for separate, independent Arab and Jewish states and establishing Jerusalem as an international city. But in the first Arab-Israeli war a year later, Israel captured western Jerusalem and Jordan took the eastern half of the city. The so-called “green line” was drawn, not as a border but a line of demarcation between Israeli and Arab forces. Jerusalem straddles that line, but in the 1967 war, Israel seized and annexed East Jerusalem, declaring Jerusalem the unified capital of the Israeli state.

The U.S. embassy has remained in Tel Aviv since it was established in 1948, with a separate consulate in Jerusalem.

"U.S. policy towards Jerusalem for decades, even predating the modern peace process, has been that Jerusalem is not a separate issue unto itself," said Yousef Munayyer, executive director of the Washington, D.C.-based U.S. Campaign for Palestinian Rights. “It’s not just a question of where do you draw a border and what happens with settlements. It’s a separate question that needs to be resolved between Israelis and Palestinians.”

Many Americans who see themselves as strong supporters of Israel also support moving the embassy to Jerusalem, to demonstrate Washington's backing of the Jewish state. Others caution that even those who support Israel should reconsider moving the U.S. embassy, because it would be a setback in the broader effort to help forge a durable peace between Israelis and Palestinians. But Trump, like many Americans, sees the move as a necessary one.

FILE - Israelis wave flags and hold signs during a rally in Jerusalem in support of Donald Trump.

"The U.S. should have all its embassies in capital cities, and Jerusalem is the capital of Israel," said Josef Olmert, adjunct professor of political science at the University of South Carolina.

"Arguing, as some do, that this is 'unilateral American action' is silly, especially when it comes from those who try to impose unilateral actions on Israel through the U.N. Security Council,” he continued, referring to calls for President Barack Obama to recognize a Palestinian state before he leaves office.

Supporters of the move say the law is on their side: In 1995, Congress passed the Jerusalem Embassy Act, acknowledging Jerusalem as Israel’s capital and calling for a new embassy to be built in that city by 1999. But there’s a catch: Built into the law is a waiver clause which allows U.S. presidents to postpone the move, six months at a time, to protect U.S. security interests.

Like Trump, former presidents Bill Clinton and George W. Bush also made campaign promises to move the embassy, but later opted to exercise the waiver every six months, concerned that it could undermine peacemaking efforts. So too has President Obama, most recently on December 1.

"Mr.Trump needs to reassert crumbling American prestige in the Middle East, which was caused by the failures of Obama’s policy,” said Olmert. “If the move will take place, President Trump will be in a better position than Obama was to try and receive meaningful concessions from [Israeli Prime Minister Benjamin] Netanyahu, having won his trust."

Maybe so, but at what cost?

“If the move does actually happen, Palestinians have to respond, and it becomes very difficult for them at that point to pretend that a Washington-mediated peace process can continue,” Munayyer said.

More worrying, he explained, is the fact that the embassy move could fit into a narrative spun by Islamist extremists, which pit Islam as engaged in a “crusade” against the West.

Moving the U.S. embassy to Jerusalem, he argues, could come across as “a triumph of Judeo-Christian civilization” over Islam.

“This is about something that really can enrage some of the most dangerous—albeit still fringe—elements in the Arab and Muslim world and become a rallying cry for extremists.”

Trump aides say the move is a “very big priority” for the president-elect. He won’t be able to transfer the U.S. mission until after June 1, when the current waiter to the Embassy Act expires.

But plans may already be underway: According to Israel’s Haaretz newspaper, Jerusalem’s mayor says U.S. officials have already begun looking for a suitable location for the new embassy—and, he said, as the Jerusalem consulate was built with an eventual move in mind, the transfer could be as simple as changing a sign on the door.